1. Field of the Invention
The present invention relates to a turbo charger bearing construction.
2. Description of the Related Art
Floating-type bearings are generally known as turbo charger bearings. A floating bearing is arranged between a turbine shaft and a bearing support on a housing (turbine housing, compressor housing) such that a thin oil film is formed between the turbine shaft and bearing and between the bearing support and bearing, and the bearing can rotate relative to the turbine shaft and bearing support. The bearing rotates relative to the turbine shaft which rotates at high speed, at a slower speed than the turbine shaft, the effect of which is to prevent for example, not only seizure due to shortage of the oil, but also to dampen and suppress turbine shaft vibration. In some turbo chargers, an oil film damper is provided on the outer circumferential side of the bearing in order to increase the rotational stability of the shaft.
FIG. 6 of the attached diagrams depicts a conventional construction of a bearing part with this type of oil film damper. A bearing 50 is interposed between a turbine shaft 56 and a bearing support 54 on the housing 52. On the inner circumferential and outer circumferential sides of the bearing 50, thin gaps 58, 60 are respectively provided, into which a lubricating oil is introduced to form an oil film damper. Oil leakage is prevented by provision of O-rings 62 adjacent to the gaps 60 on the outer circumferential side in particular.
In this conventional construction, vibration of the turbine shaft 56 is suppressed by the oil film dampers formed in the gaps 58, 60 on the inner circumferential and outer circumferential sides of the bearing 50. In order to fill the gaps 60 of this construction with sufficient oil, however, it is necessary to dispel, at the time of assembly, air held within the gaps 60, but there are problems that the air outlets are sealed by the O-rings 62, oil filling is insufficient, and the damping effect is insufficient. Meanwhile, the O-rings 62 also contribute to suppression of vibration of the turbine shaft 56, but the effect is small because its rigidity and spring force are not very great. Moreover, the bearing 50 must be precisely centered, and the thickness of the oil film damper accurately maintained, but one cannot expect the O-ring to have much effect in this respect either because of its low rigidity.